1. Field of the Invention
The invention relates to a memory device with memory cells comprising a resistive element and a selective switch and a method for reading a datum from a memory cell of a memory device comprising a resistive element.
2. Description of the Related Art
Memory cells with resistive elements and a selective switch, having for example, a solid electrolyte material as a resistive material, are well known as programmable metallization cells (PMC). Memory device including such PMC memory cells are known as conductive-bridging random access memory (CBRAM). The storing of different states in a PMC memory cell is based on the developing or diminishing of a conductive path in the electrolyte material between electrodes based on an applied electric field. Since the electrolyte material has a high resistance and the conductive path between electrodes has a low resistance, the PMC memory cell can be set to different states depending on the resistance of the PMC memory element. Usually, both states of the PMC memory cell are sufficiently time-stable in such a way that data may permanently be stored.
A PMC memory cell is operated by selectively applying a positive or a negative voltage to the solid electrolyte of the PMC memory element. In order to store data in the PMC cell, the PMC memory cell is brought to a program state by applying a suitable program voltage to the PMC memory cell which results in the development of the conductive path in the electrolyte material and therefore in the setting of a first state with low resistance. In order to store a second state in which the PMC memory cell exhibits a high resistance, an erase voltage has to be applied in such a manner that the resistance of the PMC memory cell changes back to a high resistance, which is also referred to as an erased state. To read out a datum from a PMC memory cell, a read voltage, which is lower than the programming voltage, is applied to the PMC memory cell. With the read voltage, a current through the resistance of the PMC memory cell is detected and associated to a respective low resistance state or a high resistance state of the PMC memory cell.
Conventional programming circuits for a programmable microelectronic device are known. A programming circuit is configured to provide a reversible bias across the microelectronic device to perform erase and write functions. One configuration of the programming circuit includes one or more inputs and a complementary metal-oxide semiconductor (CMOS) circuit coupled to the programmable device. This design allows for writing and erasing of the programmable cell using a low and a high voltage input. Depending on the state that should be programmed to the PMC cell, a high voltage is applied to the anode and a low voltage is applied to the cathode or, reversely, a low voltage is applied to the anode and a high voltage is applied to the cathode of the PMC cell. However, voltage cross talk may occur between the high voltage level of a selected bit line, used for programming a selected PMC cell, and a non-selected (or floating) neighbouring bit line that could cause a programming failure.